BILTEB AND GOLD PLATING. 153 



Tho objects must be dipped into this paste, or, what is 

 still, bo brushed with it; then heated on an iron plate 

 plan-d on a clear charcoal fire until they turn nearly black, and 

 finally \\asl it.'d in cold water. 



The following is another formula to the same effect : 



Sulphate of copper 3 grammes. 



Verdigris 7 



Ammonic hydrochlorate .. .. .. .. 6 



Potassic nitrate 6 



Acetic acid 31 



Pulverise the sulphate, the hydrochlorate and the nitrate, add 

 the verdigris and slowly pour the acetic acid, stirring at the 

 same time. Dip the article in the preparation and heat it 

 after on a sheet of copper until a black coloration is obtained. 

 Let it cool, then treat it with concentrated sulphuric acid. 



The article then takes a fine gold colour. 



VARIETY OP COLOUBS OF GOLD DEPOSIT. By suitably 

 mixing solutions of copper and gold, or again, solutions of silver 

 and gold, red, pink, or green gold may be obtained. 



The depositions of green gold are obtained in a bath of 

 yellow gold in good working order, and containing from 5 to 

 6 grammes of gold per litre. The electric current is maintained 

 during a few hours, a plate of pure silver being placed at the 

 positive pole. When the colour of the metal which is deposited 

 at the negative pole has reached the green tint which it is 

 desired to obtain, the operation is stopped and an anode of 

 green gold is substituted for the silver one. 



Ked gold is obtained in the same manner, by introducing 

 in an ordinary gold bath a copper anode, for which is substituted 

 a plate of alloyed gold as soon as the effect is obtained. 



INCRUSTATIONS OF GOLD AND SILVER. Messrs. Christofle 

 and Co. have succeeded in obtaining by means of electricity 

 some veritable damaskeen by incrusting gold and silver in 

 bronze, iron, and steel. 



The following is one of the methods employed by them : 



The pattern, which later on will be in gold or silver, is 

 executed in water-colour on the piece intended for incrustation. 

 Water-colour easily adheres and enables the artist to at once 



